The present invention relates to uninterrupted power supplies (UPS) and, more particularly, to a microprocessor controlled UPS wherein the microprocessor is disposed proximate the output switching circuit and is directly connected thereto.
The power supply regulators are commonly available from a variety of different sources. The most common of such devices operate to protect the connected circuit from surges in the AC power line. Such devices are limited to filter circuits disposed intermediate the AC input and the protected devices. More sophisticated circuits supplement the filter circuitry through the use of varisters, gas tubes and/or semi-conductor devices to provide greater surge protection. However, such devices do not provide means to supplement the AC input in the event that the line voltage drops below the optimum level.
Other contemporary devices extend beyond the contemporary surge protectors, providing circuitry that permit supplementing the AC input line when it drops below an optimum level. Such devices are generally of two types. The first type is commonly referred to as a standby UPS. This term is used for a UPS which provides a backup AC signal that may be interjected to the line when the line signal drops below an optimum level. One common shortcoming of such devices relates to the delay period between the time the line signal drops below the optimum level and the time that the standby AC signal is connected to the line. The resulting delay may be one cycle or less. However, where the line is connected to sensitive equipment, such as computers, the loss of even one cycle of input power can be devastating. For example, at certain times, such as when a computer is writing to a disk, the loss of power may result in significant loss of data.
A second type of UPS that permits supplementing the AC line signal, is commonly referred to as a continuous UPS. This term refers to a circuit wherein the AC line signal is converted to a DC level and later converted back to an AC signal. The backup power is supplied as a DC source, rather than an AC source as in the case of the standby UPS. The backup DC source, commonly a battery, is generally connected to the converted DC line voltage in the manner of such that when the converted DC line voltage drops below a threshhold level the backup source is connected to the line to maintain the voltage at the optimum level. An advantage of such continuous UPS devices relates to eliminating the time delay associated with the standby UPS. Because the connection between the backup DC source and the converted DC line may be effected by means of a simple diode, no inherent switching delay need occur before the backup DC source supplements the converted DC line voltage level.
One common shortcoming of continuous UPS circuits arises in connection with the switching necessary to convert the converted DC level back to an AC signal. In view of the current and voltage levels passing through the circuit the switching circuit, e.g bridge circuitry, typically generates spurious interference signals that may be induced into the switch control circuit. One common means of accommodating such spurious signals is the use of interface circuits intermediate the bridge switching circuit and the control circuit that regulates the bridge switching. The use of such interface circuitry and the need to isolate switching control circuitry from the switching circuit typically results in location of the switching control circuitry, e.g. the microprocessor, at a location remote from the switching circuitry. Consequently, the physical layout of the circuit is such that the controller is generally located on a separate card, isolated from the switching circuit by both physical distance and by means of an interface circuit.
The present invention is directed to a continuous UPS wherein the advantages of microprocessor control over the switching circuit and other circuit functions are implemented without the need to isolate the microprocessor either physically or electrically from the switching circuit. The present invention also provides for unique means for generating and controlling the UPS output signal.